linux-kernel - Re: [Part2 PATCH v6 13/38] crypto: ccp: Add Secure Encrypted Virtualization (SEV) command support

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Message-ID: <20171026201322.GA32181@nazgul.tnic>
Date:   Thu, 26 Oct 2017 22:13:22 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Gary Hook <gary.hook@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Part2 PATCH v6 13/38] crypto: ccp: Add Secure Encrypted
 Virtualization (SEV) command support

On Thu, Oct 26, 2017 at 02:26:15PM -0500, Brijesh Singh wrote:
> SHUTDOWN command unconditionally transitions a platform to uninitialized
> state. The command does not care how many processes are actively using the
> PSP. We don't want to shutdown the firmware while other process is still
> using it.

So why do you have to init and shutdown the PSP each time you execute a
command? Why isn't the PSP initialized, *exactly* *once* at driver init
and shut down, also exactly once at driver exit?

> If other process tries to issue the sev_platform_init/shutdown() then they
> have to wait.

Exactly, and not what you said earlier:

"If process "A" calls sev_platform_init() and if it gets preempted due
to whatever reason then we don't want another process to issue the
shutdown command while process "A" is in middle of sev_platform_init()."

IOW, if your critical regions are protected properly by a mutex, nothing
like the above will happen.

But what you're trying to explain to me is that the fw_init_count is
going to prevent a premature shutdown when it is > 1. But that's not
what I meant...

Anyway, see my question above.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--